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  <div class="section" id="module-imghdr">
<span id="imghdr-determine-the-type-of-an-image"></span><h1>22.7. <a class="reference internal" href="#module-imghdr" title="imghdr: Determine the type of image contained in a file or byte stream."><code class="xref py py-mod docutils literal notranslate"><span class="pre">imghdr</span></code></a> --- Determine the type of an image<a class="headerlink" href="#module-imghdr" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/imghdr.py">Lib/imghdr.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-imghdr" title="imghdr: Determine the type of image contained in a file or byte stream."><code class="xref py py-mod docutils literal notranslate"><span class="pre">imghdr</span></code></a> module determines the type of image contained in a file or
byte stream.</p>
<p>The <a class="reference internal" href="#module-imghdr" title="imghdr: Determine the type of image contained in a file or byte stream."><code class="xref py py-mod docutils literal notranslate"><span class="pre">imghdr</span></code></a> module defines the following function:</p>
<dl class="function">
<dt id="imghdr.what">
<code class="descclassname">imghdr.</code><code class="descname">what</code><span class="sig-paren">(</span><em>filename</em>, <em>h=None</em><span class="sig-paren">)</span><a class="headerlink" href="#imghdr.what" title="永久链接至目标">¶</a></dt>
<dd><p>Tests the image data contained in the file named by <em>filename</em>, and returns a
string describing the image type.  If optional <em>h</em> is provided, the <em>filename</em>
is ignored and <em>h</em> is assumed to contain the byte stream to test.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span>Accepts a <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a>.</p>
</div>
</dd></dl>

<p>The following image types are recognized, as listed below with the return value
from <a class="reference internal" href="#imghdr.what" title="imghdr.what"><code class="xref py py-func docutils literal notranslate"><span class="pre">what()</span></code></a>:</p>
<table border="1" class="docutils">
<colgroup>
<col width="26%" />
<col width="74%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Value</th>
<th class="head">Image format</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'rgb'</span></code></td>
<td>SGI ImgLib Files</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'gif'</span></code></td>
<td>GIF 87a and 89a Files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'pbm'</span></code></td>
<td>Portable Bitmap Files</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'pgm'</span></code></td>
<td>Portable Graymap Files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'ppm'</span></code></td>
<td>Portable Pixmap Files</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'tiff'</span></code></td>
<td>TIFF Files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'rast'</span></code></td>
<td>Sun Raster Files</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'xbm'</span></code></td>
<td>X Bitmap Files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'jpeg'</span></code></td>
<td>JPEG data in JFIF or Exif formats</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'bmp'</span></code></td>
<td>BMP files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'png'</span></code></td>
<td>Portable Network Graphics</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'webp'</span></code></td>
<td>WebP files</td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'exr'</span></code></td>
<td>OpenEXR Files</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">3.5 新版功能: </span>The <em>exr</em> and <em>webp</em> formats were added.</p>
</div>
<p>You can extend the list of file types <a class="reference internal" href="#module-imghdr" title="imghdr: Determine the type of image contained in a file or byte stream."><code class="xref py py-mod docutils literal notranslate"><span class="pre">imghdr</span></code></a> can recognize by appending
to this variable:</p>
<dl class="data">
<dt id="imghdr.tests">
<code class="descclassname">imghdr.</code><code class="descname">tests</code><a class="headerlink" href="#imghdr.tests" title="永久链接至目标">¶</a></dt>
<dd><p>A list of functions performing the individual tests.  Each function takes two
arguments: the byte-stream and an open file-like object. When <a class="reference internal" href="#imghdr.what" title="imghdr.what"><code class="xref py py-func docutils literal notranslate"><span class="pre">what()</span></code></a> is
called with a byte-stream, the file-like object will be <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>The test function should return a string describing the image type if the test
succeeded, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if it failed.</p>
</dd></dl>

<p>Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">imghdr</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">imghdr</span><span class="o">.</span><span class="n">what</span><span class="p">(</span><span class="s1">&#39;bass.gif&#39;</span><span class="p">)</span>
<span class="go">&#39;gif&#39;</span>
</pre></div>
</div>
</div>


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